Process for producing electrophotographic liquid developer

ABSTRACT

A PROCESS FOR PRODUCING ELECTROPHOTOGRAPHIC LIQUID DEVELOPER CONTAINING FINELY DIVIDED POWDERED POLYPEPTIDE POLYMERIC PARTICLES WHICH COMPRISES PREPARING AN INTIMATE MIXTURE OF THE SAID POLYPEPTIDE MATERIAL AND A FERROMAGNETIC POWDER MATERIAL IN AN AQUEOUS SOLUTION SUBJECTING SAID MIXTURE TO A WET PROCESS CRUSHING IN A CARRIER LIQUID AND, AFTER SAID MIXTURE IS DRIED, REMOVING SAID FERROMAGNETIC POWDER FROM SAID MIXTURE BY MEANS OF A MAGNETIC FIELD.

United States Patent 3,790,485 PROCESS FOR PRODUCING ELECTROPHOTO-GRAPHIC LIQUID DEVELOPER Masamichi Sato and Yasuo Tamai, Asaka, Japan,assignors to Xerox Corporation, Stamford, Conn. N0 Drawing. Filed Feb.3, 1972, Ser. No. 223,366 Int. Cl. G03g 9/04 U.S. Cl. 252-621 8 ClaimsABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This inventionrelates to imaging materials and more particularly to a method of makingliquid developers.

It is well known in a color reproduction process to use a liquiddeveloper containing a gelatinous material. The quality of the image andthe color prints produced therefrom is dependent to a large extent uponthe quality of the gelatinous material used, the manner of making thesame, and more specifically the ability to provide particles of fine anduniform size. Difficulties have been encountered using known processesin producing a gelatinous material of a uniformly fine particle size.

One process produces a gelatinous powder of dry pulverized gelatinousgrains. However, since grains and flakes of this material are solid,hard and tenacious, it is difficult to reduce them to a uniformly finesize. A second method includes the use of an aqueous solution of agelatinous material which is added to and dispersed in a solvent inwhich it is insoluble. Fine particles of the gelatinous material areproduced and collected from the resultant dispersion. This method,however, suffers from a shortcoming in that prior to collecting thegelatinous material from the aqueous solution, it tends to coagulate.Still another available method by which the particles of a gelatinousmaterial may be obtained is by spraying the aqueous solution of the sameinto dry air. With this method, however, it is not possible to producegelatinous particles fine enough to serve as an imaging material in aliquid developer capable of producing fine images of high resolution.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide an improved process for producing liquid developers devoid ofthe above-noted deficiencies.

It is another object of this invention to provide a novel process forproducing liquid developers containing polypeptide.

Still a further object of this invention is to provide a novel processfor polypeptide liquid developers to be used in dye printing.

Yet another object is to provide a polypeptide, material useful inmulti-color printing.

These and other objects of the present invention are accomplishedgenerally speaking by blending a polypeptide material and ferromagneticpowder material in the presence of a liquid to obtain a uniform mixture,then subjecting said mixture to a wet process crushing after dryingthereof, removing said ferromagnetic powder material from said crushedmixture by means of a magnetic field and combining said mixture with anelectrophotographic carrier.

More specifically, by adding and blending a ferromagnetic powdermaterial, e.g., ferric oxide, with a solution of a polypeptide material,e.g., bone gelatin, dissolved in water or in water and methanol, it ispossible to obtain an extremely stable dispersion because of theexcellent protective colloidal effect of the oplymeric material.Blending may be realized by means for example, of ball mill, three-rollkneader, vibrating mixer and ultrasonic dispersion. The mixture is thendried to form a cake consisting of polypeptide material andferromagnetic powder material.

Although particles or flakes consisting solely of a polypeptide materialcannot be easily crushed as explained before, the cake consisting of apolypeptide material and ferromagnetic material obtained by the presentprocess has proved to be easily crushable. The cake is then finelydivided into a powder by a wet process crushing in an electrophotographic carrier liquid or in other liquids which are imiscible with sucha carrier liquid. After being subjected to a wet process crushing, amixture of ferromagentic powder and a polypeptide material is dispersedin an organic solvent and the ferromagnetic material is removed by amagnetic field.

By using the liquid developer containing the polypeptide materialaccording to the process of this invention, a polypeptide matrix can beprepared according to the following steps:

(I) An electrostatic latent image is formed on a suitable imagingsurface such as a photoconductive insulating layer of anelectrophotographic recording member or an insulating coating of anelectrostatic recording member.

(2) The electrostatic latent image is developed by using liquiddeveloper containing the polypeptide polymeric material.

(3) The polypeptide polymeric material image thus obtained is fixed byany suitable method to form the polypeptide matrix of the printingmaster. To obtain a color print by the dye transfer method twoadditional steps are performed:

(4) An aqueous solution of a water soluble dye is brought into contactwith the polypeptide polymeric material image and the image is allowedto absorb the dye. If desired, excess dye may be removed.

(5) A separately prepared dye receiving sheet provided with a surfacelayer capable of easily absorbing the dye solution onto a polypeptidepolymeric material image is positioned so that the dye receiving layerthereof may be brought into contact with the dye absorbing polypeptideimage causing a transfer of the dye from said polypeptide image to saidsurface layer to form a final image on said dye receiving sheet.

A multiplicity of prints each carrying the dye image can be obtained byrepeating steps 4 and 5 with the same polypeptide matrix.

Any suitable polypeptide material may be used in the present invention.Typical polypeptide materials include gelatin, obtained from either hideor bone, casein glue, albumin and others. It is preferred to employgelatin with relatively narrow setting point ranges. Ordinary refinedphotographic gelatin, is found to be adequate for the purposes of thisinvention.

Any suitable ferromagnetic powdered material may be employed in theprocess of this invention. Particularly, satisfactory results areobtained with ferromagnetic substance such as iron, nickel and cobalt;metallic oxides, such as iron and chromium; ferrites, such as ironcobalt oxides, iron magnesium oxides; or alloys such as ironcobalt andiron-cobalt-nickel.

Any suitable method may be employed to fix the polypeptide imagingmatrix. A preferred method is to incorporate a resinous fixing compoundwhich is soluble in the carrier liquid.

Any suitable carrier liquid may be used in the process of thisinvention. Typically, the carrier liquid is a nonpolar highly insulativeorganic solvent substantially the same as that which is used inconventional liquid developers for electrophotography. Preferably, theelectrical resistance of the carrier liquid is greater than 10 ohmscm.Typical solvents are kerosene, decaline, cyclohexane, heptane,isooctane, gasoline and chlorofiuorinated hydrocarbons.

Any suitable amount of polypeptide material and ferromagnetic powdermaterial may be employed in the proc ess of this invention. Theferromagnetic powder material is preferably within the range of fromabout 0.1 to 10 parts by weight of said ferromagnetic powder material toabout 1 part by weight of the polypeptide material. It is believed thatthe ferromagnetic powder material cannot exhibit sufficient effect whenused in an amount less than about 01 part by weight while at the sametime the yield of the polypeptide material is lowered when the amountexceeds about 10 parts by weight.

When the liquid developer is used for developing the electrostaticlatent image, a deposition of both ferromagnetic powder material and apolypeptide material will be deposited onto the latent image. The effectof simultaneous dispersion decreases the amount of dye adsorbed on thepolypeptide relief image resulting in lowering the density of the imagein multicolor printing. The amount of polypeptide polymeric materialdeposited on a latent electrostatic image of a given electrostaticcharge density becomes lower as the content of ferromagnetic powdermaterial becomes larger. On the other hand, however, the crushing of thepolypeptide cake is considerably easier when the content of theferromagnetic powder material becomes larger. This dilemma can beprevented according to this invention by removing the ferromagneticpowder material by means of a magnetic field after the polypeptide cakeis subjected to a wet-process crushing or after the product is dilutedwith a carrier liquid. Upon subjecting the system to a magneticinfluence some polypeptide material is lost when the ferromagneticpowder material is removed, but a major portion of the polypeptidematerial remains in the dispersion. The amount of polypeptide materialremaining in the system becomes larger as the crushing time of the cakebecomes longer.

Any suitable amount of polypeptide material may be added to the carrierliquid to form the liquid developer. The concentration of polypeptidematerial in the carrier liquid is preferably within the range of fromabout 0.001 to 5% by Weight based on the weight of the carrier liquid.When the quantity of the polypeptide material particles within thecarrier liquid is extremely small, it is impossible to suificientlydevelop the electrostatic latent image on the sensitive layer. On theother hand, if the concentration of the polypeptide material is toohigh, fogging tends to occur and the dispersion stability required forthe liquid developer may deteriorate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following preferredexamples further define, describe and compare preferred materials,methods and techniques of the present invention. In the examples, allparts and percentages are by weight unless otherwise specified.

Example I 1 part by weight of photographic bone gelatin and 2 parts byweight of gamma-ferric oxide are left to stand at room temperature with30 parts by weight of water for 30 minutes, which causes the gelatinparticles to swell due to water absorption. successively, the mixture iswarmed to 60 C. to dissolve the gelatin present in said mixture. Themixture is kept at 40 C. and blended by means of a high-speed mixer forone hour to obtain a brown colored dispersion.

The brown dispersion obtained is cooled to 3 C. to obtain a coagulatedmass, which is successively cut into cubes of 1 cm. and dried, therebyobtaining brown cake consisting of gamma-ferric oxide and gelatin. Thecake thus prepared is very fragile and can be easily crushed with thefingers. 4 parts by weight of the said cake is added to a mixture of thefollowing composition and blended for 20 hours on a ball mill:

Safliower oil-modified alkyd resin 24 parts by weight Kerosene (72 partsby weight) 100 parts by weight of brown paste thus obtained is dilutedwith 900 parts by weight of kerosene.

Gamma-ferric oxide present in the brown dispersion is removed byinserting a permanent magnet into the said dispersion thereby obtaininga milk-white liquid developer.

Example II By following the same procedure as provided in Example I withthe exception that gamma-ferric oxide is removed prior to the dilutionof the brown paste with kerosene. The gelatinous particles present inthe liquid developer are found to be electrostatically charged positive.

Example III 100 parts by weight of photoconductive zinc oxide and 20parts of epoxy ester of dehydrated linseed oil fatty acids are blendedwith an adequate amount of toluene to obtain a homogeneous coatingsolution.

The coating solution is further added to 20/ 1000 parts by fiuoresceinand 20/1000 parts of tetrabromophenol blue dissolved in small amounts ofethylene glycol monomethylether in order to widen the photosensitiverange of zinc oxide to cover the whole visible wavelength range. Thecoating solution is diluted appropriately with toluene and applied on afilm microns thick) of polyethylene terephthalate previously providedwith a vacuum evaporated aluminum film, to obtain a coating of 8 micronsafter drying. After sutficient drying in a dark place, the coatedcomposition shows a satisfactory performance as an electrophotographicsensitized material.

This electrophotographic sensitized material is exposed to a negativecorona discharge in a dark place to have its surface uniformlyelectrically charged. A color slide of an original is loaded on anenlarger, with a red filter layed over the slide. The negatively chargedsensitive material is exposed to light projected through the original.

The exposed sensitive material is first wetted with kerosene and then,with minimum loss of time, soaked in the liquid developer as describedin Example I, contained in a stainless steel vat so that the vat mayfunction as the developing electrode while the surface containing theelectrostatic latent image is brought closer to the vat bottom. Afterbeing submersed is the developer for about 90 secends, the sensitivematerial is removed, Washed with isoparaifin, and then dried. Afterdevelopment, the sheet is soaked in a 1% methanol solution of formalin.The sheet is then left to stand overnight at room temperature to allowthe gelatin image to form into a hardened memher.

After the hardening treatment, the sensitive material now carrying thegelatinous image is soaked in an aqueous solution containing 40% byWeight of acetic acid for 2 minutes. This treatment caused substantiallyall of the zinc oxide present in this sensitive layer to be removed fromthe layer. The procedure to this point produces a matrix to be used forcyan printing.

Example IV By following the same procedure as provided in Example III,another sheet is exposed to light projected through the combination ofthe same original with a green filter. With the same developmenttechnique as the liquid developer containing gelatin, a matrix formagneta printing is obtained.

Example V By combining the original with a blue filter in a similarmanner as described in Example III, a matrix for yellow printing isobtained.

Example VI Each of the three matrices described in Examples III, IV andV are soaked for 2 minutes in an aqueous solution of Color Index AcidBlue 54, Acid Violet 7 and Acid Yellow 23 respectively, removed from thevats, and then washed in a bath of acetic acid.

A sheet having a gelatinous layer thereon is soaked in aluminum sulfatesolution to be mordanted and thereafter registered correctly with andpressed against the three matrices, one after another. Through thistreatment, the dyes absorbed in the toner image are transferred onto thegelatin layer. A duplicate of extremely high quality is obtained. 100duplicates are made using these matrices with substantially noalteration in print quality.

Example VII The process of Example I is followed except chromium dioxideis used instead of gamma ferric oxide to obtain similar liquid developercontaining gelatin.

In this case, chromium dioxide is employed in 3 parts by weight withrespect to 1 part by weight of gelatin, and the resulting liquiddeveloper showed the performance and results comparable to thoseobtained in Example I.

Example VIII The process of Example I is followed except that 4 parts byweight of cobalt ferrite with respect to 1 part by weight of gelatin isemployed instead of gamma ferric oxide.

The liquid developer obtained in this example shows the performances andresults comparable to those obtained in Example I.

Example IX The process of Example I is followed except 0.3 part byweight of gamma ferric oxide instead of 2 parts by weight thereof isused in order to obtain results comparable to those obtained in ExampleI.

Although specific materials and operational techniques are set forth inthe above embodiments using the developing materials and techniques ofthis invention, these are merely intended as illustrations of thepresent invention. These are other materials and techniques other thanthose listed above which may be substituted with similar results. Forexample, the wet process crushing can be preceding by a dry processcrushing. Also, in the case of wet process crushing of a carrier liquid,dispersion can be facilitated by adding resinous charge controllingagent and dispersing agents into said carrier liquid, if desirable.

Other modifications of the present invention will occur to those skilledin the art upon a reading of the present disclosure which modificationsare intended to be included within the scope of this invention.

What is claimed is:

1. A process for producing an electrophotographic liquid developercontaining finely powdered polypeptide polymeric particles comprisingthe steps of:

(a) forming an intimate mixture of one part by Weight polypeptidepolymeric particles and at least about 0.1 part by weight ferromagneticpowder in an aqueous solution;

(b) drying the aqueous solution to form cakes;

(c) forming a dispersion from said cakes by pulverizing said cakes intoa finely divided powder by blending said cakes in a liquid dispersioncomprising an organic carrier liquid and;

(d) removing said ferromagnetic powdered material from said dispersionby means of a magnetic field.

2. The method of claim 1 wherein the carrier liquid has an electricalresistivity greater than 10 ohms-cm.

3. The method of claim 1 wherein said pulverizing is performed bywet-crushing. I

4. The method of claim 1 wherein said organic carrier liquid is anon-polar, highly insulating organic solvent.

5. The method of claim 1 wherein said polypeptide is selected from thegroup consisting of gelatin, casein glue, and albumin.

6. The method of claim 1 wherein said ferromagnetic powder is selectedfrom the group consisting of iron, nickel, cobalt, iron oxide, chromiumoxide, ferrites and alloys thereof.

7. The method of claim 1 wherein the ratio of ferromagnetic powder topolypeptide is from about 0.1 to 1 to about 10 to 1 parts by weight.

8. The method of claim 1 wherein said organic carrier liquid is selectedfrom the group consisting of kerosene, decaline, cyclohexane, heptane,isooctane, gasoline, and chlorofiuorinated hydrocarbons.

References Cited UNITED STATES PATENTS 2,183,084 12/1939 Reynolds 2601182,197,843 4/1940 Van Leesuven 61-36 2,527,268 10/1950 Hart et al. 72,754,292 7/1956 Henderson et a1. 260 2,826,571 3/1958 Henika et a1260-415 3,137,630 6/1964 Hecker et a1 16781 3,682,825 8/1972 T amai etal 25262 .1 3,692,523 9/ 1972 Tamai et al 252-621 J. TRAVIS BROWN,Primary Examiner J. P. BRAMMER, Assistant Examiner US. Cl. X.R. 260-112,118

